The present invention relates to a method of correcting proximity effects occurring in pattern formation based on direct writing by a charged-particle beam or light exposure in the course of a semiconductor manufacturing process.
A technique for fine and high-density formation of patterns in semiconductor integrated circuit devices employs a charged-particle beam exposure apparatus for formation of patterns through direct writing or an optical reduced-projection exposure apparatus for formation of patterns through light exposure. In this formation procedure, dimensional accuracy of patterns is degraded o account of proximity effects, and it is indispensable to correct the patterns for proximity effects in order to improve the dimensional accuracy.
Generally, there are several available methods of correcting proximity effects. In one, a pattern is divided into a plurality of rectangular or triangular element figures and suitable amounts of electron irradiation are assigned to respective figures. In another, original pattern data is treated in advance in expectation of the fact that eventual patterns distorted by proximity effects have desired pattern shapes and dimensions.
FIG. 16 is a flow chart showing a conventional technique of proximity effect correction and FIG. 17 is a diagram useful to explain the FIG. 16 technique. Referring to FIG. 17, reference numeral 1 designates the cell boundary of the uppermost cell A, 2 the cell boundary of a cell B belonging to a second hierarchy, 3 and 4 the cell boundaries of the lowermost cells C, and 5 to 10 patterns in the cells. Conventionally, operations for correction of the aforementioned proximity effects are carried out as follows. Design data of patterns in cells having a hierarchical structure as shown in FIG. 17A are inputted to a computer for performing proximity effect correction operations (STEP 1), and part of the inputted data for the underlaid cells B and C is developed onto the uppermost cell A so that all patterns behave as though they belong to the same hierarchical level (STEP 2). The uppermost cell A subjected to the development is divided by the dividing line, as designated at 11, into a plurality of rectangular sub-zones as shown in FIG. 17B and each sub-zone is surrounded by a reference frame zone 12 (dotted zone in the drawing) having a width h equaling a typical length affected by proximity effects (STEP 3). Operations are carried out for a pattern (or patterns) in each sub-zone and element figures, in that sub-zone, of a pattern (or patterns) which partly belongs to that sub-zone and is cut at the boundary thereof, by looking up proximity effects which are caused by a pattern (or patterns) and element figures in the reference frame zone 12 (STEP 4), and the results of correction are obtained (STEP 5). For example, reference may be made to J. Appl. Phys. 50 (1979), PP 4371 to 4387.
The prior art method, however, faces problems that the disc capacity for ensuring the working file necessary to process large-scale and highly-integrated patterns and the time for processing are drastically increased, and the conventional method can not be used in practical applications.